Adsorption of lecithin lipids and proteins at air/aqueous and aqueous/solid interfaces

Tze Lee Phang, Purdue University

Abstract

The goal of this research is to develop a fundamental understanding of the adsorption of lipids and proteins at various interfaces. The results of the adsorption of dilauroylphosphatidylcholine (DLPC) lipid and serum proteins at the air/water interface shows that DLPC lipid is able to generate low surface tensions even in the presence of the serum proteins. Moreover, DLPC is able to expel an already adsorbed serum protein layer from the interface. Before the serum protein is displaced by DLPC at the interface, there is a substantial initial enhancement in the protein adsorption, consistent with some interaction or binding of DLPC with protein to produce a more hydrophobic protein surface. After the protein molecules have been displaced by DLPC, protein molecules are less favored to adsorb near the DLPC monolayer with the lecithin headgroups facing towards them. The results have implications for possible uses of DLPC lipid in potential lung surfactant formulations in treating patients with ARDS. ^ A new method of Physically Self-Assembled Monolayers (PSAMs) for lipid monolayer films on hydrophilic silica surfaces has been developed. It fabricates high quality monolayers by allowing the lipids to be physically adsorbed and self assemble onto the hydrophilic surfaces. The lipid is dissolving in a mixture of a nonpolar and a strong polar solvent. The surface densities of the adsorbed layers are limited to monolayers, and can be varied by changing the concentration of the polar solvent. The PSAMs method has many advantages compared to Langmuir-Blodgett and chemically SAMs methods. ^ The effect of protocols of lipid dispersions preparation on the generation and stability of liposomes or vesicles has been studied. When DLPC dispersions are stirred vigorously, the liposomes size generally decreases. There is also evidence of unilamellar vesicles. When these dispersions are sonicated extensively until they look transparent, mostly polydisperse, small unilamellar vesicles form. Nonetheless, the cryo-transmission electron microscopy reveals clear evidence of some small liposomes. These results are important for lung surfactant replacement applications, because the liposome or vesicle sizes affect the dynamics of surface tension. They also are relevant in designing liposome-based or vesicle-based drug delivery vehicles for respiratory or cancer therapies. ^

Degree

Ph.D.

Advisors

Elias I. Franses, Purdue University.

Subject Area

Chemistry, Biochemistry|Engineering, Chemical

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